1. Field of the Invention
The invention relates to a semiconductor device fabrication method, particularly to patterning of a Mn-based perovskite-type oxide.
2. Description of Related Art
Giant magnetoresistance effect means considerable change of the electric resistance when magnetic field is applied and has been found in a metal artificial lattice Fe/Cr. Successively, the giant magnetoresistance effect has been found also in artificial lattices of Co/Cu and many (Fe, Co, or Ni, or their alloys)/(a noble metal such as Cu, Ag or Au, Cr, or a transition metal such as Ru). Today, along with investigations on mechanism of the giant magnetoresistance effect, investigations on its application have enthusiastically been made. With respect to the application of the giant magnetoresistance effect, for the purpose of the soft magnetic giant magnetoresistance effect, investigations of giant magnetoresistance multilayer thin films utilizing retention difference and magnetic anisotropy have been advanced. Spin valve giant magnetoresistance expected to be highly possible for utilization to magnetoresistance heads for reading high density magnetic recording is a typical representative for that.
Conventionally, the giant magnetoresistance effect has been found in metal-based materials. However, materials having the giant magnetoresistance effect have been found among Mn-based perovskite-type oxide series.
In recent years, the electric resistance properties of the Mn-based perovskite-type oxide materials have been found to be changeable by applying one or more electric pulses to thin films or bulk materials. Accordingly, the Mn-containing oxides are expected to be applicable for nonvolatile memories (reference to Japanese Unexamined Patent Publication Nos. 2003-68983, 2003-68984, and 2003-197877).
For applications to nonvolatile memories, it is required to form fine devices and therefore, thin film formation techniques of Mn-based perovskite-type oxides are indispensable. As thin film formation methods there are physical methods such as a vacuum evaporation method, a sputtering method, a laser abrasion method and the like and chemical methods such as a sol-gel method and MOCVD (Metal Organic Chemical Vapor Deposition) for obtaining oxide ferroelectrics from organometal compounds as starting materials by thermally decomposing and oxidizing the materials and the like.
Chemical mechanical polishing methods (CMP methods) have generally been employed for patterning the Mn-based perovskite-type oxide materials.
Here, a semiconductor device fabrication method described in Japanese Unexamined Patent Publication No. 2003-197877 will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view showing fabrication steps of a conventional semiconductor device.
At first, a patterned oxide film 53 is formed on an underlayer 51. Next, an oxide layer 55 of a Mn-based perovskite-type oxide is formed so as to cover the oxide film 53 to obtain the structure shown in FIG. 2(a). Next, the oxide layer 55 is abraded until the oxide film 53 is exposed by a chemical mechanical polishing method so as to obtain a patterned oxide layer 55 (FIG. 2(b)).
However, generally, the Mn-based perovskite-type oxides have high solubility in common etching solutions of acidic solutions or organic solvents and therefore, patterning using such etching solutions is difficult and conventionally, chemical mechanical polishing methods have been employed.
Accordingly, as described above, chemical mechanical polishing methods have been employed, however in the case of the methods, the process steps are many and complicated and as a result, the process cost is high. Further, in general, each process step inevitably generates defective products (every step has a certain failure ratio) and thus the yield is decreased more as more process steps are performed.
Therefore, as a simple and easy method, patterning of the Mn-based perovskite-type oxide materials is desirable to be carried out by wet etching using an etching solution.
In the case of using Mn-based perovskite-type oxides for memory devices, fine pattern formation by dry etching is inevitable in future. In such a case, a large quantity of etching residues are left at the time of etching the Mn-based perovskite-type oxides and these residues form leak paths to cause adverse effects on the memory yield. Accordingly, residue treatment using chemical solutions is required, and also in such a case, the Mn-based perovskite-type oxides are easily dissolved in the chemical solutions for the residue treatment to result in defective shape such as film separation and decreased yield.